In photonics circuitry, thermo-optic phase shifters are often used as optical bias or tuning elements, such as in modulators or in tunable filters. Generally, an improved efficiency of thermo-optic phase shifters can be desirable for producing smaller and/or low-power optical devices, as well as for providing a greater tuning range within a given power budget.
One technique for improving the efficiency of a thermo-optic phase shifter includes placement of a distinct heating element in close proximity to the optical waveguide, which reduces an amount of heat that is coupled into other nearby elements, such as a substrate. However, the close proximity of the heating element tends to increase an optical insertion loss. Another technique for improving the efficiency of the thermo-optic phase shifter includes thermally isolating the heating element and/or optical waveguide from other elements (e.g., the substrate) using air trenches or other thermally insulative material(s).
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.